In recent years, molecules of oligosaccharides have attracted attention as third chain life molecules following nucleic acids (DNA) and proteins. The human body is a huge cell society comprising about 60 trillion cells, and the surfaces of all the cells are covered with oligosaccharide molecules. For example, ABO blood groups are determined according to the difference of oligosaccharides over the surfaces of cells.
Oligosaccharides function in connection with the recognition of cells and interaction of cells and are key substances for the establishment of the cell society. Disturbances in the cell society lead, for example, to cancers, chronic diseases, infectious diseases and aging.
For example, it is known that when cells cancerate, changes occur in the structure of oligosaccharides. It is also known that Vibrio cholerae, influenza virus, etc. ingress into cells and cause infection by recognizing and attaching to a specific oligosaccharide.
Oligosaccharides are much more complex than DNA or proteins in structure because of the diversity of arrangements of monosaccharides, modes or sites of linkages, lengths of chains, modes of branches and overall structures of higher order. Accordingly, biological information derived from the structures thereof is more diversified than is the case with DNA and proteins. Although the importance of research on oligosaccharides has been recognized, the complexity and variety of structures thereof have delayed progress in the research on oligosaccharides unlike the studies on DNA and proteins.
On the other hand, it is known that asparagine-linked oligosaccharides are obtained from delipidated egg yolk (see, for example, Patent Literature 1). According to Patent Literature 1, asparagine-linked oligosaccharides are obtained in larger quantities than conventionally by adding almond or apricot seed to delipidated egg yolk. However, this process provides asparagine-linked oligosaccharides which are 95% or 92% in purity, failing to isolate pure asparagine-linked oligosaccharides. As to the yield, 100 kg of delipidated egg yolk affords 29.5 g or 27.2 g of a disialyloligosacchride (disialylundecasaccharide).
It is also known that a glycopeptide (SGP: sialylglycopeptide) extracted from a soluble fraction of chicken eggs affords asparagine-linked oligosaccharides. The SGP is a compound wherein an asparagine moiety of a peptide chain comprising six moieties of amino acids is linked to the reducing terminal of a composite oligosaccharide comprising eleven sugar moieties. However, the process of Seko et. al [Biochemica Biophysica Acta, Vol. 1335, p. 23(1997)], for example, yielded only about 8 mg of SGP from one chicken egg yolk.
[Patent Literature 1] WO96/02255 (claims 8 and 10)
An object of the present invention is to provide a process for preparing asparagine-linked oligosaccharide derivatives by which various isolated asparagine-linked oligosaccharide derivatives can be obtained in larger quantities and with much greater ease than conventionally for use in the field of developing pharmaceuticals or the like.